How Does An Electron Microscope Work?

How Does An Electron Microscope Work?

Electron microscopes have revolutionized scientific imaging, revealing nanoscale details. In this post, we’ll explore their capabilities, including scanning electron microscopes (SEMs), transmission electron microscopes (TEMs), and scanning transmission electron microscopes (STEMs). We'll also review the components of an electron microscope and the average cost. In a separate post, we compare the differences of a light microscope vs. electron microscope if you're interested in learning or reviewing their similarities and differences.

What Does an Electron Microscope Do?

Optical microscopes or light microscopes aren’t good enough to see bacteria, viruses, or molecules. Instead, we rely on electron microscopes to see these things in nano-dimensions. Electron wavelengths can be up to 100,000 times shorter than the wavelength of visible light photons so electron microscopes have a much higher resolution and make it possible to see the structure of smaller objects.

Electron microscopes are most commonly used to research the ultrastructure of biological and inorganic specimens such as biopsy samples, crystals, metals, microorganisms, and cells. They can also be used industrially to help with quality control and failure analysis. Today’s modern electron microscopes produce micrographs with specialized digital cameras and frame grabbers to capture the image of the specimen.

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How Does an Electron Microscope Work?

Like an optical microscope, there are four important parts, but with some differences. Instead of a light source, an electron microscope features an electron source, a beam of electrons powered by a filament.

The specimen needs to be prepared and held inside a vacuum chamber where there is no air. Electrons are easily scattered by air particles that include gas molecules like oxygen and nitrogen, so without a vacuum the electron beam would be knocked off of it’s course. Biological samples can evaporate immediately in a vacuum without preparing the sample ahead of time, so it is important to take some preparative steps.

Instead of lenses, you have a series of electromagnets the electron beam travels through, referred to as electromagnetic lenses. With an ordinary microscope, the glass lenses either bend or refract the light beams passing through them to magnify the specimen. With an electron microscope, the coil-shaped electromagnets bend the beams the same way.

Instead of looking through an eyepiece to see the magnified sample, the microscope image is formed as a photograph, also known as an electron micrograph, or displayed on a computer screen.

Different types of electron microscopes are on the market and each of them works in a slightly different way. All produce high-resolution images, though some types are better suited for certain materials than others.

Types of Electron Microscopes

Transmission Electron Microscope (TEM)

A transmission electron microscope (TEM) is also known as the original form of the electron microscope. It uses a high-voltage electron beam to illuminate the specimen and produce a flat image.

The beam is made by an electron gun that is commonly filled with tungsten filament as the source. They’re commonly used in electron diffraction mode but often require incredibly thin sections about 100 nanometers thick for the electrons to pass through.

Creating specimens this thin is often extremely difficult and technically challenging. Some specimens may require dehydration or chemical fixation before cutting into thin slices is even possible. Some also may need to be stained for easier visibility.

Serial-Section Electron Microscope (ssEM)

An ssEM Is a subset of TEM. It creates images of many thin sections in sequence.

Scanning Electron Microscope (SEM)

A scanning electron microscope (SEM) is similar to a key copying machine. When you get a key copied, the machine traces over the original key to cut an exact replica into a blank. The copy isn’t produced all at once but instead traced out from one end to the other. The specimen under examination can be considered the original key.

The SEM uses an electron beam to trace the object and create an exact replica of the original on a monitor. Instead of just tracing out a flat outline of the key, the SEM provides a 3D image that’s complete with grooves and engraving.

As the beam traces over the object and interacts with the surfaces to dislodge secondary electrons from the surface of the specimen in patterns. A secondary detector attracts those electrons.  The number of electrons that reach the electron detector influences the brightness level shown on the monitor.

Reflection Electron Microscope (REM)

With a reflection electron microscope (REM), an electron beam is on a surface, but instead of using the transmission or secondary electrons, the beam of elastically scattered electrons is detected.

This type of microscopy is used to observe processes happening on a sample’s surface. The elastically scattered electrons hit the sample at different glancing angles, which in turn generates an image.

Scanning Transmission Electron Microscope (STEM)

A scanning transmission electron microscope (STEM) creates images with a focused beam of electrons on an incredibly small area on the specimen, typically .05 to .2 nanometers. It is then scanned over the sample in a raster illumination system so that the sample is illuminated at each point with the beam parallel to an optical axis.

This type of electron microscopy is suitable for analytical techniques. The typical STEM microscope is a conventional TEM microscope that has additional scanning coils, detectors, and circuitry to allow it to switch between operating as a STEM or a standard TEM. However, it is also possible to find dedicated STEMs.

Scanning Tunnelling Microscopy (STM)

STM microscopes create detailed images of the molecules or atoms on the surface of the sample. They work differently than TEM and SEM.

STM microscopes use an extremely sharp metallic probe that scans back and forth across the surface of a specimen. Electrons try to move out of the specimen and jump across the gap into the probe. The closer the probe is to the surface, the easier it is for the electrons to move into it and as more electrons escape, the greater the tunneling current becomes.

The microscope constantly moves the probe up and down by minuscule amounts to keep the tunneling constant. By recording how much the probe needs to move it measures the peaks and valleys throughout the specimen’s surface.

A computer converts this information into a map of the specimen that reveals its detailed atomic structure. Ordinary electron microscopes use high-energy electron beams to produce their highly detailed images but the intensity tends to damage the object they are imaging. STM uses lower energies to reduce the likelihood of damage.

Atomic Force Microscope (AFM)

One of the disadvantages of STM’s is that they rely on the electrical currents passing through materials to create their images. If the object is not a conductor of electricity, the microscope cannot create an image.

Atomic force microscopy (AFM) microscopes don’t have this problem because even though they still use tunneling, they are not reliant on a current flowing between the probe and the specimen. Using this type of microscope makes it possible to create atomic-scale images of plastics and other materials that do not conduct electricity.

Cryo-Electron Microscopy (Cryo-EM)

Also known as cryo-EM, this involves using frozen samples with gentler electron beams to work with samples that aren’t compatible with high-vacuum conditions and intense electron beams.

Recently, a special method to freeze water-based TEM samples was developed so that the water creates a disordered glass instead of crystalline ice. Ice crystals diffract the electron beam and obscure information about the molecules.

Cryo-EM eliminates this issue and makes it possible to use transmission electron microscopy with samples incompatible with a vacuum environment.

How Much Do Electron Microscopes Cost?

The price of an electron microscope can vary widely depending on several factors. Price varies according to the type you purchase as well as what you intend to use it for and your final configuration. Different detectors and resolutions are available that you may or may not need, dependent on your application.

On the low end of the spectrum, a fairly basic tabletop scanning electron microscope (SEM) would cost around $50,000 to $70,000. These tabletop models are suitable for educational institutions or smaller research labs that require moderate imaging capabilities.

Moving up the scale, a conventional SEM with a tungsten source, which offers higher resolution and more advanced imaging capabilities, could easily cost anywhere from $80,000 to $120,000. These systems are commonly used in research settings, particularly in material science, where detailed surface imaging is crucial.

For specialized applications, or when higher resolutions and additional features are required, the cost can escalate significantly. Transmission electron microscopes (TEM) and scanning transmission electron microscopes (STEM) are examples of advanced electron microscopy systems that provide atomic-level imaging capabilities. These instruments are essential for studying ultra-fine details of biological samples, nanoparticles, and crystalline structures. A high-end TEM or STEM can range from hundreds of thousands to several million dollars.

Beyond the initial purchase cost, it's important to consider other expenses associated with maintaining and operating an electron microscope. This includes costs for consumables such as electron microscope grids, sample preparation materials, and any specialized detectors or accessories that may be required for specific experiments.

To sum it up: the price of an electron microscope is influenced by factors like the type of microscope, intended applications, and the level of resolution and features needed. A basic tabletop SEM starts at around $50,000 to $70,000, while more advanced models with higher resolution capabilities can range from $80,000 to $120,000. Specialized TEM and STEM instruments can cost several hundred thousand to several million dollars. It's important for potential buyers to carefully assess their specific needs and budgetary constraints before making a purchase.

Leasing vs. Buying Electron Microscopes

Leasing an electron microscope can be a highly advantageous option for many labs, especially those where a substantial upfront investment in equipment isn't financially feasible. Excedr offers a compelling solution by providing access to the electron microscopes your lab requires, all without the burden of a significant upfront capital expenditure. This allows your lab to allocate funds to other critical research endeavors.

One of the key benefits of leasing through Excedr is that it not only covers the cost of the equipment but also includes maintenance and repair coverage as part of the lease agreement. That said, the coverage is optional. Some researchers opt out of this coverage to reduce their monthly payments, but service coverage can be highly beneficial. With proper service coverage in place, you can focus on your research without the worry of unexpected expenses for upkeep. Furthermore, you reduce unexpected downtime in the case of equipment breakdowns.

Simply put, this comprehensive package ensures that your electron microscope remains in optimal working condition, contributing to the efficiency and productivity of your lab.

Excedr's leasing options extend beyond electron microscopes. If your lab requires a diverse range of microscopy tools, Excedr offers leasing services for x-ray microscopes, infrared microscopes, confocal microscopes, fluorescence microscopes, Raman microscopes, and multi-photon microscopes. This flexibility allows your lab to access a suite of cutting-edge microscopy equipment tailored to your specific research needs.

By choosing to lease, you not only gain access to top-of-the-line equipment, but you also benefit from the convenience and cost-effectiveness of a comprehensive leasing package. This can be particularly advantageous for labs with budget constraints or cash runway concerns, and for those looking to allocate resources strategically across various research endeavors.

Excedr's equipment leasing program provides an attractive alternative to outright purchasing of electron microscopes. Contact us today to learn more about how Excedr's equipment leasing program can revolutionize your lab's capabilities.